The present invention relates generally to temperature sensors. More specifically, the present invention relates to intelligent input/output (I/O) temperature sensors. Advantageously, a corresponding method for calibrating the intelligent I/O temperature sensors is also disclosed.
Numerous devices for remotely sensing temperatures, particularly temperatures reflecting the operational parameters of various machines and machine systems have been produced. In recent years, numerous programmable temperature sensors have become available. For example, U.S. Pat. No. 5,781,075 to Bolton, Jr. et al., which is entitled "Temperature Sensing Apparatus," discloses a programmable temperature sensor supplied with both a biasing current and a voltage from a temperature independent voltage source. In this apparatus, the output voltage generated by the voltage source is programmable; thus, the output of the temperature sensor can be adjusted by programming the output voltage of the temperature independent voltage source. It will be appreciated that temperature sensors utilizing the patented circuit exhibit a significant part count, particularly when it is desirable to output the temperature data in digital form. The latter would require at least an analog-to-digital converter (ADC), since the patented circuit generates an analog output. U.S. Pat. Nos. 5,241,850 and 5,519,354 disclose alternative circuitry for programming the temperature range of a temperature sensor; this circuitry also suffers from the same problems.
When installed in a temperature sensing system where the temperature has to sensed from a plurality of locations, it is often expedient to compensate all of the sensors, not individually at the sensor location but at the controller of the temperature sensing system. This requires not only the storage of temperature compensation data for each sensor at the controller but that the controller dedicate a significant portion of its processing time to correcting temperature data gathered by the temperature sensing system.
U.S. Pat. No. 5,444,637 to Smesny et al., which is entitled "Programmable Semiconductor Wafer For Sensing, Recording and Retrieving Fabrication Process Conditions To Which The Wafer Is Exposed," discloses a programmable semiconductor wafer device 10, which, as illustrated in FIG. 1, includes numerous circuits formed upon its surface topography to sense, store and retrieve processing conditions exerted upon the wafer. Circuits include sensors 12 placed within select regions 14 configured across the surface of wafer 10. Each region 14 includes at least one sensor 12 and preferably many sensors capable of reading one or numerous processing conditions. A sensor within each region is configured to detect a single processing condition. If more than one sensor is formed within each region, then numerous processing conditions can be detected based upon the number of sensors so formed. Sensors 12 reads, stores and retrieves one or many processing conditions registered within each region 14 and across the semiconductor wafer. Regions 14 are disposed substantially equi-distant from one another across the entire wafer surface in order to obtain an accurate gradient reading thereon. In FIG. 1, four sensors 12 are placed within each of seven regions 14.
Placed between select regions 14 is a semiconductor power device 16, i.e., either photoelectronic conversion device or a direct electrical storage device using conventional capacitor arrays or a thin film lithium battery. Placed between select regions 14 and spaced from power supply 16 is a signal acquisition/conditioning circuit 18 and a processor 20 containing read only as well as read/write memory. Acquisition/conditioning circuit 18 is connected between processor 20 and each sensor 12 contained within each region 14. Circuit 18 provides a data-conversion function, while processor 20 contains digital components which perform computer and/or peripheral interfacing tasks. Acquisition/conditioning circuit 18 includes circuitry necessary to accommodate the input or sensor voltage of each sensor 12 into a digital signal acceptable for processor 20. To transform the analog signal from each sensor 12 to a digital data stream acceptable by processor 20, a multiplex circuit as well as an A/D converter and amplifier is needed as part of circuit 18. Furthermore, to increase the speed at which the information can be accurately converted, a S/H circuit may also be used as part of circuit 18 to compress analog signal information.
Coupled to acquisition/conditioning circuit 18, as well as processor 20, is an external control circuit 22 which can be arranged in one or more locations between regions 14 as would be necessary to maximize the use of semiconductor real estate. External control circuit 22 is capable of receiving programmable input from an external device and, based upon that input, provide timing pulses, enables, etc., to circuit 18 as well as processor 20. Input indicia into external control circuit 22 is provided via an input probe pad 24. Pad 24 is a conductive, substantially planar structure connected to the input of circuit 22 similar to a bonding pad arrangement normally associated with the periphery of an integrated circuit die. Pad 24 is of sufficient size to allow repeated mechanical alignment and contact with an external probe source. Probe pad 24 allows data to be input into circuit 22 necessary for programming and reprogramming of processor 20. Wafer 10 also includes an output probe pad 26, which is configured similar to input probe pad 24 for allowing mechanical access from an external output device necessary for receiving digital information stored within the read/write memory of processor 20.
The wafer sensor system described immediately above suffers from both of the problems discussed above. First, the system has an unacceptably high part count, by virtue of such elements as the multiplexer, signal conditioning filters and ADCs. Moreover, the processor receives raw data from the sensors, in spite of the fact that the data signals are conditioned a number of times on their way between the sensors and the processor. It will be noted that the data storage associated with the system comprises a central data store.
What is needed is a stand alone temperature sensor that provides both accuracy and linearity compensation. Moreover, what is needed is a stand alone temperature sensor providing storage of historical data, where the storage device is some form of non-volatile memory. Furthermore, what is needed is a stand alone temperature sensor which can be easily linked with a plurality of other stand alone temperature sensors via a serial bus to form a temperature sensor system. Lastly, it would be advantageous to have a temperature sensing system wherein each of the stand alone temperature sensors can be re-programmed over the aforementioned serial bus.